In the field of optical switches, several designs are known in the art. These switches can be categorized into two separate classes.
The first class of optical switches relies on reflected radiation within the switch. These devices, such as those proposed by Sauer in U.S. Pat. No. 4,340,813, and Uberbacher in the IBM Technical Disclosure Bulletin of July 1975, Volume 18, No. 2, page 483, are dependent on the physical motion of a component, such as a surface membrane, to alter the optical path within the component. By so doing, the switching characteristics are effected.
These designs have several known shortcomings. First, while they are immune to external optical radiation, the area of actuation or touch/sense point is extremely limited. Further, these approaches require constraints on manufacturing tolerances. Moreover, these designs do not provide an extension to proximity sensing. Finally, they fail to provide an option of the actuation surface and the switch mechanism.
The second class of optical switches, such as those proposed by Bergstrom in U.S. Pat. Nos. 4,254,333 and 4,814,600, as well as Udalov et al. Soviet Union Patent Number 636,803, depend on the frustration of total internal reflection ("FTIR"). These devices require physical contact with a reflecting surface to interrupt the internal reflection of an optical light beam.
As with the first class of switches, FTIR switches have several inherent limitations. First, FTIR devices are sensitive to external light sources, such as ambient light, as well as dirt, oil films, water and other contaminants. These materials form on an actuation surface of an FTIR switch, thereby reducing switching threshold and causing false actuations. Moreover, the switching reliability of FTIR devices is known to be sensitive to nature quality of the contacting object. Thus, a gloved finger may not respond as an ungloved finger might. Furthermore, these devices have tight manufacturing tolerances. FTIR type switches have areas of restricted actuation. Similarly, these devices lack a simple method for separating the actuation plane from the switch mechanism or a method for extending the switch to proximity sensing.
As such, there remains a need for an optical switch having substantial immunity to external optical radiation and contaminants impacting the actuation surfaces. A demand further exists for an optical switch which can be enabled irrespective of the quality and nature of the contacting object. An optical switch is moreover needed having substantially reduced manufacturing tolerances. Likewise, a demands exists for an optical switch having extended proximity sensing. Furthermore, a need exists for an optical switch having a substantially increased area of actuation. There is also presently a demand for an optical switch having the capability of separating the actuating surface from the switch mechanism. Likewise, there is a demand for the actuating surface to be backlit for visibility and actuation indication.